once vimception, always vimception

[florian-wagner]

Great stuff @ivanov ! This plugin completes the perfect working environment for me.

One thing I noticed: If I load the extension once in a notebook, vimception writes all kinds of stuff to the notebook file, which ist not reversible even if the cell loading the extension is deleted. This means once I tried out the extension in a notebook, this notebook gets always loaded with vimception enabled and syntax highlighting is always missing (issue #10).